1. Field of the Invention
The present invention is directed to aerosol cans and, more particularly, to aerosol cans constructed of aluminum.
2. Description of the Background
Traditionally, beverage cans begin as disks of aluminum coil feedstock that are processed into the shape of a beverage can. The sides of these cans are approximately 0.13 mm thick. Generally, the body of a beverage can, excluding the top, is one piece.
In contrast, aerosol cans are traditionally made one of two ways. First, they can be made from three pieces of steel, a top piece, a bottom piece, and a cylindrical sidewall having a weld seem running the length of the sidewall. These three pieces are assembled to form the can. Aerosol cans may also be made from a process known as impact extrusion. In an impact extrusion process, a hydraulic ram punches an aluminum slug to begin forming the can. The sides of the can are thinned to approximately 0.40 mm through an ironing process that lengthens the walls of the can. The rough edges of the wall are trimmed and the can is passed through a series of necking dies to form the top of the can. Although aerosol cans made of steel are less expensive than aerosol cans made by an impact extrusion process, steel cans are aesthetically much less desirable than aerosol cans made with an impact extrusion process.
For a variety of reasons, aluminum aerosol cans are significantly more expensive to produce than aluminum beverage cans. First, more aluminum is used in an aerosol can than in a beverage can. Second, the production of aluminum cans by impact extrusion is limited by the maximum speed of the hydraulic ram of the press. Theoretically, the maximum speed of the ram is 200 strokes/minute. Practically, the speed is 180 slugs/minute. Beverage cans are made at a rate of 2,400 cans/minute.
One problem facing the aerosol can industry is producing an aluminum aerosol can that performs as well or better than traditional aerosol cans but is economically competitive with the cost of producing steel aerosol cans and aluminum beverage cans. Another problem is producing an aerosol can that has the printing and design quality demanded by designers of high-end products. Traditional beverage cans are limited in the clarity of printing and design that can be imprinted on the cans. Beverage cans are also limited in the number of colors that can be used in can designs. Thus, a need exits for an aluminum aerosol can that has the attributes of strength and quality, while being produced at a cost that is competitive with steel aerosol cans.
Producing aluminum cans of a series 3000 aluminum alloy coil feedstock solves some of these problems. Series 3000 aluminum alloy coil feedstock can be shaped into a can using a reverse draw and ironing process, which is significantly faster and more cost effective than impact extrusion, aluminum can production. Additionally, series 3000 aluminum alloy is less expensive, more cost effective, and allows for better quality printing and graphics than the use of pure aluminum.
Unfortunately, certain obstacles arise in necking a series 3000 aluminum alloy can. Series 3000 aluminum alloy is a harder material than pure aluminum. Therefore, cans made from series 3000 aluminum alloy are stiffer and have more memory. This is advantageous because the cans are more dent resistant, but it poses problems in necking the cans by traditional means because the cans stick in traditional necking dies and jam traditional necking machines. The solution to these obstacles is embodied in the method of the present invention.